Our research is directed to the study of the integrative function of gastrointestinal hormones and related peptides. The three main functions of the hormones are being investigated using a variety of in vivo and in vitro preparations: 1. Transport of electrolytes and water in canine small intestine (isolated loops); in gastric fistula dogs: isolated stripped gastric mucosae and sacs and isolated colonic sacs (rat). Each preparation has some advantage for the study of secretory stimulant or inhibitory effect of hormones. 2. Muscle contraction (gall bladder, small intestine) in response to GI hormones: emphasis in this instance being placed on the interaction of cholecystokinin and secretin-like hormones. 3. The release of pancreatic hormones (insulin, glucagon) by GI hormones in vivo (dog and cat) and in vitro (slices of pancreas from the mouse). The present emphasis in these studies is to determine the interplay of neural-hormonal and hormonal-hormonal mechanisms in order to simulate as nearly as possible the conditions prevailing in the body.